Method and apparatus for etch passivating and etching a substrate

ABSTRACT

A substrate having a patterned mask and exposed openings is provided in a process chamber having process electrodes. In a plasma ignition stage, a process gas is provided in the process chamber and is energized by maintaining the process electrodes at a plasma ignition bias power level. In an etch-passivating stage, an etch-passivating material is formed on at least portions of the substrate by maintaining the process electrodes at an etch-passivating bias power level. In an etching stage, the exposed openings on the substrate are etched by maintaining the process electrodes at an etching bias power level.

CROSS-REFERENCE

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/414,329, filed on Oct. 6, 1999, entitled “Method andApparatus for Etching a Substrate with Reduced Microloading,” which isincorporated herein by reference in its entirety.

BACKGROUND

[0002] The present invention relates to etching of a substrate in aplasma of process gas.

[0003] Electronic devices, such as integrated circuits, are formed bydeposition, growth (such as by oxidation, nitridation, etc.) and etchingof material on a substrate. In a typical etching process, a patternedetch-resistant mask is formed on the substrate by a conventionalphotolithographic process, and thereafter, exposed portions of thesubstrate are etched away with energized gases. In the etching process,a reactive gas is introduced into a chamber and is supplied withelectromagnetic energy, such as microwave or radio frequency energy, toform an energized gas, such as a plasma, to etch the substrate. Inaddition, a biasing voltage may be applied to the plasma to energizecharged plasma species to provide more anisotropic etching.

[0004] In the etching process, it is desirable to control the dimensionsof the features being etched, and it also desirable to etch features,such as openings or trenches, with smooth vertical sidewalls. However,conventional etching processes often result in non-uniform etching ratesand microloading effects across the substrate. Microloading is a generalterm used to describe undesirable variations in etch rates, featureshapes, or other etching attributes, from one etched feature to anotherand across the substrate. For example, the etching rates of the etchedholes may vary between small diameter holes which have a high aspectratio and large diameter holes or open spaces. As another example, theshape or etching rates of the etched features may vary from regions ofthe substrate having a high density of features (dense feature regions)to regions having relatively few and isolated features (isolated featureregions). Critical dimension microloading may also arise from thevariations in critical dimensions of the etched features, the criticaldimensions (CD) being those dimensions that are used to calculate theelectrical properties of the etched features in the design of integratedcircuits. For example, the cross-sectional area of an interconnect lineor contact is a critical dimension that should be close to predetermineddimensions to provide the desired electrical resistance.

[0005] Accordingly, it is desirable to etch features, such as holes andinterconnect lines, across the substrate at uniform and reproducibleetch rates. It is further desirable to reduce variations in the etchingrate of the high aspect ratio holes relative to open spaces on thesubstrate. It is also desirable to obtain etched features having uniformand predictable shapes.

SUMMARY

[0006] A method of processing a substrate in a process chamber havingprocess electrodes comprises providing a substrate in the processchamber, the substrate comprising a patterned mask and exposed openings,in a plasma ignition stage, providing a process gas in the processchamber and energizing the process gas by maintaining the processelectrodes at a plasma ignition bias power level, in an etch-passivatingstage, forming an etch-passivating material on at least portions of thesubstrate by maintaining the process electrodes at an etch-passivatingbias power level, and in an etching stage, etching the exposed openingson the substrate by maintaining the process electrodes at an etchingbias power level.

[0007] A substrate processing apparatus comprises a process chamberhaving a support capable of receiving a substrate, wherein the substratecomprises a patterned mask and exposed openings, a gas supply capable ofintroducing a process gas into the process chamber, a gas energizer toenergize the process gas, the gas energizer comprising processelectrodes, and a controller adapted to (i) in a plasma ignition stage,maintain the process electrodes at a plasma ignition bias power level toignite a plasma, (ii) in an etch-passivating stage, maintain the processelectrodes at an etch-passivating bias power level to form anetch-passivating material on at least portions of the substrate, and(iii) in an etching stage, maintain the process electrodes at an etchingbias power level to etch the exposed openings on the substrate.

DRAWINGS

[0008] These and other features, aspects, and advantages of the presentinvention will be better understood from the following drawings,description and appended claims, which illustrate exemplary features ofthe invention; however, it is to be understood that each of the featurescan be used in the invention in general, not merely in the context ofthe particular drawing, and the invention includes any combination ofthese features:

[0009]FIGS. 1a through 1 c (prior art) illustrate schematic sectionalside views of a substrate etched by a prior art etching method;

[0010]FIGS. 2a through 2 c illustrate schematic sectional side views ofa substrate etched by a method according to the present invention;

[0011]FIG. 3 is a flow chart showing the process steps in an embodimentof a method according to the principles of the present invention;

[0012]FIG. 4 is a schematic timing diagram of a set of processconditions that illustrate the method of FIG. 3;

[0013]FIG. 5 (prior art) is a schematic timing diagram of processconditions used in a typical prior art process; and

[0014]FIG. 6 is a schematic illustration of an embodiment of a processchamber useful for practicing the present invention.

DESCRIPTION

[0015] The method and apparatus of the present invention are useful fordepositing etch-passivating material on a substrate, and thereafter,etching the surface of the substrate, to reduce etch-rate microloadingand providing more anisotropic etching. By “substrate” it is meant asupport and overlying layers composed of semiconductor, dielectric andmetal-containing or conductor materials. The substrate is typically awafer of silicon, gallium arsenide or silica glass; the semiconductormaterial on the substrate may include, for example, n or p-doped regionsof polysilicon or silicon; the dielectric layers may include, forexample, silicon dioxide, undoped silicate glass, phosphosilicate glass(PSG), borophosphosilicate glass (BPSG), Si₃N₄, or TEOS deposited glass;and the metal-containing or conductor layers may include, for example,aluminum, copper, tungsten silicide or cobalt silicide.

[0016] An exemplary substrate 20, as schematically illustrated in FIGS.1a, comprises a surface 22 bearing an overlying pattern ofetch-resistant features 24 comprising photoresist and/or hard mask(typically silicon oxide or silicon nitride) which are formed byconventional photolithographic methods. The etch-resistant features 24on the surface 22 of the substrate 20 may be spaced apart from oneanother to expose large openings 26 of the surface of the substrate orclosely spaced to expose small openings 28. The large openings 26 have arelatively large solid angle (β) as compared to the solid angle (α) ofthe small openings 28. It has been discovered that as the smalleropenings 28 get smaller in size relative to the larger openings 26, andvice versa, conventional etching processes result in a more pronounceddifference in etching rates between the larger and smaller openings, asillustrated in FIGS. 1b and 1 c. It is believed that this occurs becausethe smaller openings 28 are approaching sizes that are sufficientlysmall—which may be as small as 0.35 micron or less—that the size of theopening, as determined by the solid angle (α) of the opening, becomes alimiting factor in the accessibility of etching plasma species intothese openings. In contrast, the relatively large solid angle (β) of thelarge openings 26 provides greater accessibility of plasma species intothese openings to allow a relatively larger population of plasma ionsand other species to bombard the substrate 20 during the etchingprocess. As a result, the small openings 28 are etched at slower etchrates than the large openings 26. This results in etching ratemicroloading in which the etched features 25 may be etched to differentdepths across the substrate 20, which is undesirable.

[0017] The present invention may be used to overcome these problems andprovide reduced microloading effects across the substrate 20. In oneembodiment, as illustrated in the flow chart of FIG. 3, multiple stagesare used to initially treat or process the substrate 20 to achieve thedesired etching results. These stages include initial preparatory stages32, 34, a plasma ignition stage 36, a plasma stabilization stage 38, adeposition stage 40, and a plasma etching stage 42. Each of these stagesis described below. However, it should be understood that the processmay comprise fewer or additional stages, and that the stages may becombined with one another, as would be apparent to one of ordinaryskill. Accordingly, the scope of the present method should not belimited to the illustrative embodiments described herein.

[0018] In the initial stages 32, 34, a process zone is evacuated to alow pressure, and a substrate 20 is transported into the process zone.Referring to FIG. 4, in the initial or plasma ignition stage 36, a gasis introduced into the process zone, and a pressure 46 of the gas is setto a desired ignition pressure level 46 a. For plasma ignition, theignition gas pressure level 46 a is typically from about 50 to about 200mTorr. The gas is suitable for igniting the plasma and is typically anon-reactive gas, such as argon, and may also include a reactive gas,such as an etchant gas that is used to process the substrate 20. Thenon-reactive gas may be used to form or stabilize the initial plasmastate before the etchant gas is introduced into the pre-energizedplasma. The gas in the process zone is energized to a plasma state bycapacitively or inductively coupling electromagnetic energy to the gas.For example, the plasma may be ignited by capacitively coupling energyto the gas by applying a bias voltage at an initial or plasma ignitionbias power level 50 to process electrodes in the process zone. Theignition bias power level 50 may be controlled by the voltage appliedacross electrodes located above, around, and/or below the substrate 20.Generally, the initial or ignition bias power level 50 a is at leastabout 150 Watts, and more typically from about 150 to about 500 Watts.In this stage, the source power level 48 a is typically set to a lowignition source level 48 a which may be zero. Also, typically, theetchant gas flow level 44 a is typically zero, but etchant gas may beintroduced at this stage. The high bias power level is maintained for ashort time of a few seconds to ignite the plasma.

[0019] In the plasma stabilization stage 38, a higher source power level48 b of electromagnetic energy is inductively coupled to the energizedgas in the process zone while the bias power 50 is maintained at a lowerstabilization level 50 b, which may include turning off the bias powerlevel altogether. The source power level 48 b controls the inductivelycoupled power applied to the energized gas to stabilize and sustain theplasma, and it is the power level of the current applied to an antennadisposed about the process chamber. The inductively coupled RF energysupplied from the antenna is used to stabilize and maintain a plasma inthe process chamber, and the level of stabilization source power canalso effect the reactivity of the plasma. During this stage, thestabilization source power level 48 b is typically set to between about2000 and about 4000, and more preferably 2000 Watts. In addition, thegas pressure 46 is reduced to a lower level 46 b in the mTorr range, forexample, about 10 to about 30 mTorr. The etchant gas 44 is held at aflow level 44 b of zero.

[0020] Thereafter, in a deposition stage 40, the process conditions ofthe energized gas are set to form deposits 30 from the energized gasonto the surface 22 of the substrate 20, as illustrated in FIGS. 2athrough 2 c. The deposits 30 may be composed of etch-passivatingmaterial that provides some resistance to etching by the etchant gas.The etch-passivating deposits 30 typically contain a fluoropolymercomprising fluorine and carbon species. Alternatively, the deposits 30may comprise other materials, including materials that remain on thesubstrate 20 after processing and may also comprise materials that areused to form various layers on the substrate 20, such as for example,dielectric, semiconductor, metal or conductor, or other materials.

[0021] The etch-passivating deposits 30 that are formed on the surface22 of the substrate 20 slow down the rate of etching at those portionsof the substrate 20, thereby provide etched features 27 having sidewallswhich are more perpendicular and less tapered, i.e., with enhancedanisotropic etching, as schematically shown in FIG. 2c. Preferably,thicker deposits 30 are formed in the larger sized openings 26 (as shownin FIG. 2b), which causes the exposed surfaces 22 of the substrate 20within the larger openings 26 to be etched slower than the exposedsubstrate 20 in the smaller openings 28. This compensates for the higheretch rates obtained in the larger openings 26 that occurred in prior artetching processes. As a result, low etch-rate microloading is obtainedin which the depth of the etched features 27 do not significantlychange, whether in an isolated region of the substrate 20 which has fewfeatures 27 with large openings 26 or in a dense region of the substrate20 which has a large number of features 27 with smaller openings 28. Byforcing increased deposition of etch-passivating material in the largeopenings 26 of the substrate 20, the etching microloading effects uponcompletion of the etch process were found to be significantly reduced.Accordingly, the substrate 20 is etched more uniformly and with reducedetch-rate microloading.

[0022] To form the etch-passivating deposits 30, gas that is capable offorming passivating deposits is introduced into the process zone in thedeposition stage. In general, these deposits may be formed by thegaseous species reacting with itself or other reactive species in theplasma, such as gaseous species originating from the material on thesubstrate 20. The gas that forms the etch-passivating deposits 30 mayalso be capable of etching the substrate 20, i.e., the gas may alsocomprise the etchant gas. Good control of microloading is obtained whenthe reactant gas contains a fluorocarbon gas such as CF₄, C₂F₆, CHF₃,CH₂F₂, and CH₃F, which may also serve as the etchant gas for etchingthrough a silicon-containing material. In the stage 40, the etchant gasflow 44 is typically increased to from about 2 to about 500 sccm. Forexample, the gas may comprise (i) about 20 to about 60 sccm CHF₃ andabout 100 to about 300 sccm argon, or (b) about 2 to about 250 sccmC₂F₆, and more preferably, 20 to 50 sccm C₂F₆; about 1 to about 150C₂H₂F₂, and more preferably, 20 to 50 sccm CH₂F₂; and about 10 to about1500 sccm argon, and more preferably, 50 to 200 sccm argon. The gaspressure 46 is typically set to a deposition pressure level 46 c whichis higher than the stabilization pressure level 46 b, but lower than theignition pressure level 46 a, such as for example, from about 10 toabout 100 mTorr.

[0023] In addition, the bias power level 50 is maintained at adeposition bias power level 50 c that is sufficiently low to allow etchpassivating deposits 30 to form on the substrate 20. The deposition biaspower level 50 c at which etch-passivating deposits 30 are formeddepends on the other process conditions such as the composition andpressure of the gas, the source power level 48, and the temperature ofthe substrate 20. Increasing the deposition bias power level 50 cincreases the energy of the plasma ions impacting the surface 22 of thesubstrate 20 and reduces the thickness of the etch-passivating deposits30 formed on the substrate 20. Reducing the deposition bias power level50 c reduces the rate of removal of the etch-passivating deposits 30,especially in the large openings 26 of the substrate 20 that have fewfeatures. In one version, the deposition bias power level 50 c ismaintained at less than about 100 Watts, and more preferably from about10 to about 50 Watts. The bias power level 50 c may also be desirablyreduced to a zero level by shutting off the voltage applied to theprocess electrodes and letting both electrodes float at the chamberpotential. Typically, the deposition bias power level 50 c is maintainedat a reduced level for about 2 to about 24 seconds, and more typicallyfor about 8 to about 16 seconds. Generally, it is desirable to apply avoltage to the electrode monotonically, i.e., by maintaining a biaspower level over the entire electrode surface, rather than, for example,only on a portion of the electrode. The uniform voltage across theentire electrode below the substrate 20 uniformly energizes the plasmaions above the substrate 20. During the deposition stage 40, the sourcepower level 48 is also reduced to a lower deposition level 48 c thanthat used in the earlier plasma stabilization stage 38, and is typicallyfrom about 800 to about 2000 Watts.

[0024] After formation of the etch-passivating deposits 30, thesubstrate 20 is etched in an etching process stage 42. In the etchingstage 42, additional etchant gas may be introduced into the processzone, or the etchant gas may be the same gas as that used to ignite theplasma. The composition of the etchant gas depends upon the compositionof the material to be etched. For example, in the etching ofsilicon-containing materials—such as for example, silicon, polysilicon,or silicon dioxide—the etchant gas often comprises a fluorine-containinggas such as a fluorocarbon gas such as CF₄, C₂F₆, CHF₃, CH₂F₂, and CH₃F.During the etching stage 42, the flow rate 44 b of etchant gas istypically from about 10 to about 100 sccm. The gas pressure 46 is set tothe same or a different level 46 d than that of the earlier stage, suchas for example, from about 5 to about 100 mTorr. After the gascomposition has stabilized, the process conditions of the energized gasare set to etch the surface 22 of the substrate 20.

[0025] In the etching stage 42, the bias power level 50 is increased toan etching bias power level 50 d which is higher than the previousdeposition bias power level 50 c in the deposition stage 40. The higheretching bias power level 50 d provides anisotropic etching of thesubstrate 20. Preferably, the etching bias power level 50 d ismaintained at a sufficiently low level to allow formation of someetch-passivating deposits 30 on the substrate 20 during the etchprocess. These deposits 30 protect the sidewalls of the etched features27 from being excessively etched in the horizontal direction, therebyproviding anisotropic etching with vertical and non-tapered sidewalls.Typically, the etching bias power level 50 d is set to from about 800 toabout 1600 Watts. In addition, the source power 48 is maintained at anetching source power level 48 d that is lower than the stabilizationsource power level 48 c, and is typically from about 800 to about 2000Watts. The etching stage 42 is typically conducted for about 0.5 toabout 10 minutes, and more preferably from about 2 to about 3 minutes.

[0026] The process of the present invention allows etching of asubstrate 20 with etch-rate microloading of less than about 15%, oftenless than 10%, and sometimes less than 5%. These are significantlyimproved microloading results. In addition, it should be further notedthat the etching step is conducted in the same process zone as that inwhich the etch-passivating deposits were formed. In contrast, prior artchambers typically deposit and etch material in different process zonesand in different process chambers. Although multiple chambers may beutilized to conduct the process of the present invention, it is oftenfaster to utilize a single process chamber to conduct each stage of theprocess because the substrate does not have to be moved from one chamberto another at each process stage.

[0027] As a comparative example, FIG. 5 shows a schematic of a processcondition timing diagram of a prior art etching process. In the priorart etching process, the bias power 58 was increased to a higher level58 a at the same time as when the etchant gas flow 52 a was started inthe etching stage 55. There is no deposition stage, and instead, theprior art process comprises a plasma ignition stage 51, a plasmastabilization stage 53, and an etching stage 55. It was discovered thatthe increased bias power level 58 a reduced the formation of theetch-passivating deposits 30 on the substrate 20 during the etchingstage. It is believed that the high bias power level 58 a energize theplasma ions, causing the plasma ions to energetically bombard thesubstrate 20, thus preventing the etch-passivating deposits from formingon the substrate 20. It was further discovered that in the largeopenings 26 of the substrate 20, the removal of the etch-passivatingdeposits by the energetic plasma was even more pronounced than in thesmaller openings 28. This resulted in little or no formation ofetch-passivating deposits in the larger openings 26 of the substrate 20relative to the smaller openings 28. As a result, during the subsequentetching process, large etch-rate microloading effects were observed withdifferences in etch rate of up to 20% between the large openings 26 andthe small openings 28. These microloading effects were reduced tonegligible levels by the method and apparatus of the present invention.

EXAMPLES

[0028] The following examples illustrate use of the present inventionfor etching of a substrate in a plasma of process gas. However, theapparatus and method can be used in other applications as would beapparent to those skilled in the art, and the scope of the presentinvention should not be limited to the illustrative examples providedherein.

[0029] In these examples, substrates were processed in an IPS chamber,schematically illustrated in FIG. 4, and commercially available fromApplied Materials Inc., Santa Clara, Calif. The apparatus 100 comprisesan enclosed process chamber 110 defining a process zone 115 forprocessing the substrate 20, and a support 120 having a receivingsurface 125 for holding the substrate 20 during processing. A load-locktransfer area (not shown) is maintained at low pressure for holding acassette of substrates. The enclosed chamber 110 has walls 130fabricated from a metal, ceramic, glass, polymer, or composite material,and which may have a surrounding liner. The process zone 115 of theetching chamber is above and around the substrate 20 and typicallycomprises a volume of at least about 10,000 cm³, and more typically fromabout 10,000 to about 50,000 cm³. The particular embodiment of theapparatus 100 shown herein is suitable for processing of semiconductorsubstrates, is provided only to illustrate the invention, and should notbe used to limit the scope of the invention.

[0030] Process gas is introduced into the chamber 110 by a gas supply140 that includes a gas source 145 and a gas flow controller 150 thatregulates the gas flow through one or more gas flow control valves 155.The gas is provided in the chamber 110 via gas nozzles 160 located at oraround the periphery of the substrate 20 (as shown), or which may beprovided in a showerhead on the ceiling of the chamber (not shown).Preferably, the gas is introduced through a ring 165 that is maintainedat a temperature of from about 250° C. to about 400° C. Spent processgas and etchant byproducts are exhausted from the process chamber 110through an exhaust system 170 (typically including roughing and highvacuum-type exhaust pumps 175) capable of achieving a minimum pressureof about 10⁻³ mTorr in the chamber 110. A throttle valve 180 is providedin the exhaust to control the flow of spent process gas and the pressureof process gas in the chamber 110.

[0031] A plasma may be generated from the process gas introduced intothe chamber 110 using a plasma generator 185 that couples anelectromagnetic energy into the gas in the process zone 65 of thechamber 55. A suitable plasma generator 185 comprises an antenna 190adjacent to the ceiling 200 consisting of one or more coils 195 having acircular symmetry with a central axis coincident with the longitudinalvertical axis that extends through the process chamber 110. The ceiling200 is of material which admits electromagnetic fields generated by theantenna 190 into the process zone 65. This material may be a dielectricor as described below a semiconductor. The frequency of the RF voltageapplied to the antenna 190 is typically from about 50 KHz to about 60MHz, and more typically about 2 MHz, and the power level of RF voltageapplied to the antenna 190 is typically from about 100 to about 5000Watts.

[0032] Instead, or in addition to the antenna 190, the plasma generator185 may comprise one or more process electrodes 210, 215 that may beused to accelerate or energize the plasma ions in the chamber 110. Forexample, the process electrodes may include a first electrode 210comprising a wall of the process chamber, such as the ceiling 200 of thechamber. The first electrode 210 is capacitively coupled to a secondelectrode 215 in the support 120 below the substrate 20. The secondelectrode 215 is fabricated from a metal such as tungsten, tantalum, ormolybdenum, and may be covered by or embedded in a dielectric 220. Thesecond electrode 215 may serve as an electrostatic chuck 225 thatgenerates an electrostatic charge for electrostatically holding thesubstrate 20 to the receiving surface 125 of the support. A heater orcooler (not shown) may also be provided below the dielectric 220 to heator cool the overlying substrate 20 to suitable temperatures.

[0033] In a preferred embodiment, the first electrode 210 comprises asemiconductor ceiling 200 that is sufficiently electrically conductiveto be biased or grounded to form an electric field in the chamber 110yet provides low impedance to an RF induction field transmitted by theantenna 190 above the ceiling 200. Many well-known semiconductormaterials can be employed, such as silicon carbide, germanium, or GroupIII-V compound semiconductors such as gallium arsenide and indiumphosphide, or Group II-III-V compound semiconductors such asmercury-cadmium-telluride. However, a ceiling comprising silicon ispreferred since it is less likely to be a source of contamination forprocessing silicon substrates, in comparison with other materials. Morepreferably, the semiconductor ceiling 200 comprises semiconductingsilicon having a resistivity of less than about 500 Ω-cm (at roomtemperature), and most preferably about 20 Ω-cm to about 200 Ω-cm. Thetemperature of the ceiling is typically maintained at from about 120° C.to about 200° C., and often above about 300° C.

[0034] The first and second electrodes 210, 215 are electrically biasedrelative to one another by the electrode voltage supply 230 thatincludes an AC voltage supply for providing a plasma generating RFvoltage to the second electrode 215, and a DC voltage supply forproviding a chucking voltage to the second electrode 215. The AC voltagesupply provides an RF generating voltage having one or more frequenciesfrom 50 KHz to 60 MHz, and preferably about 2 MHz. The power level ofthe RF bias current applied to the electrodes 200, 215 is typically fromabout 50 to about 3000 Watts. When the second electrode 215 also servesas an electrostatic chuck, a separate DC voltage is applied to theelectrode 215 to form an electrostatic charge that holds the substrate20 to the chuck. The RF power is coupled to a bridge circuit and anelectrical filter to provide DC chucking power to the electrode 215.

[0035] Typically, the apparatus 100 is operated by one or morecontrollers (not shown) that include instructions to set first processconditions to form etch-passivating deposits onto a surface of thesubstrate, and set second process conditions to etch the surface of thesubstrate. Typically, the controller comprises a computer operating acomputer program containing program code embodying the processconditions. For example, the program code may comprise computerinstructions to lower a bias power applied to the process electrodesafter a plasma of the gas is stabilized, to set a bias power ofsubstantially zero, or to maintain a bias power at a predetermined leveland for a preset time. In addition, the program code may comprisecomputer instructions to maintain a flow of a gas capable of formingetch-passivating deposits on the substrate or etching the substrate,control a source power level applied to an inductor source about theprocess zone, or change a bias power level to another bias power level.

[0036] In the example, substrates 20 comprising silicon wafers having apattern of etch-resistant features 24 thereon were processed. Thepatterned etch-resistant features 24 included trenches with smallopenings 28 sized about 0.5 micrometers (μm) and trenches with largeopenings 26 sized about 5 μm, which is about ten times higher.

[0037] The chamber 110 was initially pumped down to a pressure of about10⁻⁴ Torr, and argon gas at a flow rate of 200 sccm was introduced intothe chamber 110. The pressure of the gas was stabilized at about 50mTorr. The temperature of the second electrode 215 was held at about−10° C., the temperature of the ceiling 200 maintained at about 140° C.,and the temperature of the ring 165 at about 270° C.

[0038] In the plasma ignition stage, a plasma was ignited from the gasby applying an RF bias voltage at an ignition bias power level of 370Watts to the process electrodes 210, 215 in the chamber 110. In theplasma stabilization stage, the bias power level was turned off, and asource power level of 1200 Watts was applied to the antenna 190 tosustain the plasma by an inductive energy. Thereafter, the plasma wasstabilized for 10 seconds.

[0039] In the etch-passivation deposit stage, a gas composition of 25sccm C₂F₆/15 sccm CH₂F₂/150 sccm Ar was introduced into the chamber 110,and a pressure of 60 mTorr was maintained. The source power was reducedto 1000 Watts.

[0040] The deposition stage was operated for time intervals of 0, 8, or16 seconds. Thereafter, the substrates 20 were etched in an etchingstage, the bias power level to the electrodes 210, 215 was turned up toa higher level of about 800 Watts, while the source power was maintainedat 1000 Watts. Each substrate 20 was etched for 150 seconds. By varyingthe amount of time that a substrate 20 was exposed to thefluorocarbon-containing plasma in the absence of an applied biasvoltage, the effects of the etch-passivating deposits on the subsequentetching process were evaluated.

[0041] In the first example, the deposition stage was not used, andinstead the bias power was turned on at the same time as the etchant gaswas introduced as with a conventional prior art process. After etching,the substrates 20 were cut, and cross-sections of the etched openingswere examined by scanning electron microscopy (SEM). The SEMmicrophotographs showed an etch depth of 1.9 μm in the small openings 28as compared with an etch depth of 2.27 μm in the large openings 26. Thisevidenced a microloading effect (PD) of about 16% between the small andlarge openings, as determined from:$\mu_{o} = {\frac{{E_{o}\quad {open}\quad {area}} - {E_{c}\quad {contact}\quad {hole}}}{E_{o}\quad {open}\quad {area}} \times 100\%}$

[0042] where E_(o) open area is the etch depth obtained in featureshaving large openings 26, and E_(c) contact is the etch depth obtainedin features having small openings 28.

[0043] In the second example, the deposition stage was operated for 8seconds after the etchant gas was introduced. The SEM micrographs of theetched substrates showed an etch depth of 2.43 μm in the small openings28 as compared with an etch depth of 2.8 μm in the large openings 26.This demonstrated a reduced microloading of about 13% which was about25% less than the microloading obtained in the first example.

[0044] In the third example, the deposition stage was operated for about16 seconds after the etchant gas was introduced. The microphotographsshowed an etch depth of 2.55 μm in the small openings 28 as comparedwith an etch depth of 2.6 μm in the large openings 26. Thus microloadingof less than 5% was obtained. The close to 60% improvement inmicroloading over the non-deposition prior art process was an unexpectedand surprising result.

[0045] The present invention has been described with reference tocertain preferred versions thereof; however, other versions arepossible. For example, the invention has been described with referenceto a preferred etching process and chamber. However, the inventiveprocesses can be applied in other process chambers as would be apparentto one of ordinary skill, including without limitation, CVD and PVDprocess chambers. Therefore, the spirit and scope of the appended claimsshould not be limited to the description of the preferred versionscontained herein.

What is claimed is:
 1. A method of processing a substrate in a processchamber having process electrodes, the method comprising: (a) providinga substrate in the process chamber, the substrate comprising a patternedmask and exposed openings; (b) in a plasma ignition stage, providing aprocess gas in the process chamber and energizing the process gas bymaintaining the process electrodes at a plasma ignition bias powerlevel; (c) in an etch-passivating stage, forming an etch-passivatingmaterial on at least portions of the substrate by maintaining theprocess electrodes at an etch-passivating bias power level; and (d) inan etching stage, etching the exposed openings on the substrate bymaintaining the process electrodes at an etching bias power level.
 2. Amethod according to claim 1 wherein the etch-passivating bias powerlevel is lower than the plasma ignition bias power level.
 3. A methodaccording to claim 2 wherein the etch-passivating power level is lowerthan the plasma ignition bias power level by at least about 200 Watts.4. A method according to claim 1 comprising maintaining theetch-passivating bias power level at less than about 100 Watts.
 5. Amethod according to claim 4 comprising maintaining the etch-passivatingbias power level at from about 10 to about 50 Watts.
 6. A methodaccording to claim 4 comprising maintaining the etch-passivating biaspower level at substantially zero.
 7. A method according to claim 1comprising maintaining the etch-passivating bias power level for fromabout 0 to about 16 seconds.
 8. A method according to claim 1 whereinthe etching bias power level is higher that the etch-passivating biaspower level.
 9. A method according to claim 1 comprising maintaining theetching bias power level at from about 800 to about 1600 Watts.
 10. Amethod according to claim 1 wherein the patterned mask comprisesphotoresist.
 11. A method according to claim 1 wherein the patternedmask comprises hard mask.
 12. A method according to claim 1 comprisingproviding a process gas comprising a fluorocarbon gas.
 13. A methodaccording to claim 12 wherein the fluorocarbon gas comprises one or moreof CF₄, C₂F₆, CH₂F₂, CH₃F and CHF₃.
 14. A method according to claim 1wherein the process gas comprises a non-reactive gas.
 15. A methodaccording to claim 1 further comprising lowering a source power levelapplied to an inductor antenna about the process chamber to form theetch-passivating material.
 16. A substrate processing apparatuscomprising: a process chamber having a support capable of receiving asubstrate, wherein the substrate comprises a patterned mask and exposedopenings; a gas supply capable of introducing a process gas into theprocess chamber; a gas energizer to energize the process gas, the gasenergizer comprising process electrodes; and a controller adapted to (i)in a plasma ignition stage, maintain the process electrodes at a plasmaignition bias power level to ignite a plasma, (ii) in anetch-passivating stage, maintain the process electrodes at anetch-passivating bias power level to form an etch-passivating materialon at least portions of the substrate, and (iii) in an etching stage,maintain the process electrodes at an etching bias power level to etchthe exposed openings on the substrate.
 17. An apparatus according toclaim 16 wherein the controller is adapted to lower the plasma ignitionbias power level to the etch-passivating bias power level.
 18. Anapparatus according to claim 17 wherein the controller is adapted tolower the plasma ignition bias power by at most about 200 Watts.
 19. Anapparatus according to claim 16 wherein the controller is adapted tomaintain an etch-passivating bias power of at less than about 100 Watts.20. An apparatus according to claim 19 wherein controller is adapted tomaintain an etch-passivating bias power level of from about 10 to about50 Watts.
 21. An apparatus according to claim 19 wherein the controlleris adapted to maintain an etch-passivating bias power level ofsubstantially zero.
 22. An apparatus according to claim 16 wherein thecontroller is adapted to maintain the etch-passivating bias power levelfor from about 0 to about 16 seconds.
 23. An apparatus according toclaim 16 wherein the controller is adapted to maintain the etching biaspower level at from about 800 to about 1600 Watts.
 24. An apparatusaccording to claim 16 wherein the controller is adapted to lower asource power level applied to an inductor antenna about the processchamber to form the etch-passivating material.